In a series of 960 cases comprising almost all cases of colorectal carcinoma diagnosed intra vitam during a 10‐year period in a defined population, there were 62 (6.5%) patients with multiple primary colorectal carcinoma. The average annual incidence was 2.6/100,000 inhabitants. Males were affected more often than females, and the frequency of patients with coexisting adenomas was higher than that in the parent series. The survival rates did not differ from those in the parent series. Synchronous lesions were seen twice as often as metachronous lesions, but the frequency of the latter is regarded as provisional. The findings suggest an interrelationship between colorectal adenoma and carcinoma. It may be concluded that every case of colorectal carcinoma requires a thorough preoperative examination of the entire large intestine. It is also concluded that all patients with colorectal carcinoma operated upon for cure should be regularly followed up for the rest of their lives for metachronous carcinomas. Cancer 33:1630–1634, 1974.